Add camera backend tests and fixtures

Add comprehensive tests for camera backends: aravis and OpenCV (tests/cameras/backends/*). Introduce a backend-specific pytest conftest that detects optional dependencies, provides --run-hardware gating, and supplies fixtures to reset registry or force fake/unavailable SDKs. Include extensive fake Aravis/OpenCV helpers to exercise read/open/close/configure paths. Also apply two tiny tweaks: add a file-identifying comment in dlclivegui/cameras/factory.py and remove an unused bbox_color parameter from tests/conftest.py.

Author: C-Achard

dlclivegui/cameras/factory.py

@@ -1,5 +1,6 @@
 """Backend discovery and construction utilities."""
 
+# dlclivegui/cameras/factory.py
 from __future__ import annotations
 
 import copy

tests/cameras/backends/conftest.py

@@ -0,0 +1,120 @@
+# tests/cameras/backends/conftest.py
+import importlib
+import os
+
+import pytest
+
+
+# -----------------------------
+# Dependency detection helpers
+# -----------------------------
+def _has_module(name: str) -> bool:
+    try:
+        importlib.import_module(name)
+        return True
+    except Exception:
+        return False
+
+
+ARAVIS_AVAILABLE = _has_module("gi")  # Aravis via GObject introspection
+PYPYLON_AVAILABLE = _has_module("pypylon")  # Basler pypylon SDK
+
+
+# -----------------------------
+# Pytest configuration
+# -----------------------------
+def pytest_addoption(parser: pytest.Parser) -> None:
+    parser.addoption(
+        "--run-hardware",
+        action="store_true",
+        default=False,
+        help="Run tests that require hardware/SDKs (aravis/pypylon/gentl). "
+        "By default these are skipped. You can also set BACKENDS_RUN_HARDWARE=1.",
+    )
+
+
+def pytest_configure(config: pytest.Config) -> None:
+    # Document custom markers
+    config.addinivalue_line("markers", "hardware: tests that touch real devices or SDKs")
+    config.addinivalue_line("markers", "aravis: tests for Aravis backend")
+    config.addinivalue_line("markers", "pypylon: tests for Basler/pypylon backend")
+
+
+def pytest_collection_modifyitems(config: pytest.Config, items: list[pytest.Item]) -> None:
+    """
+    Auto-skip tests if the corresponding dependency is not present,
+    and only run hardware-marked tests when explicitly requested.
+    """
+    run_hardware_flag = bool(config.getoption("--run-hardware"))
+    run_hardware_env = os.getenv("BACKENDS_RUN_HARDWARE", "").strip() in {"1", "true", "yes"}
+    run_hardware = run_hardware_flag or run_hardware_env
+
+    skip_no_aravis = pytest.mark.skip(reason="Aravis/gi is not available")
+    skip_no_pypylon = pytest.mark.skip(reason="Basler pypylon is not available")
+    skip_hardware = pytest.mark.skip(
+        reason="Hardware/SDK tests disabled. Use --run-hardware or set BACKENDS_RUN_HARDWARE=1"
+    )
+
+    for item in items:
+        # Per-backend availability skips
+        if "aravis" in item.keywords and not ARAVIS_AVAILABLE:
+            item.add_marker(skip_no_aravis)
+        if "pypylon" in item.keywords and not PYPYLON_AVAILABLE:
+            item.add_marker(skip_no_pypylon)
+
+        # Global hardware gate (only applies to tests marked 'hardware')
+        if "hardware" in item.keywords and not run_hardware:
+            item.add_marker(skip_hardware)
+
+
+# -----------------------------
+# Useful fixtures for backends
+# -----------------------------
+@pytest.fixture
+def reset_backend_registry():
+    """
+    Ensure backend registry is clean for tests that rely on registration behavior.
+    Automatically imports the package module that registers backends.
+    """
+    from dlclivegui.cameras.base import reset_backends
+
+    reset_backends()
+    try:
+        # Import once so decorators run and register built-ins where possible.
+        import dlclivegui.cameras.backends  # noqa: F401
+    except Exception:
+        # If import fails (optional deps), tests can still register backends directly.
+        pass
+    yield
+    reset_backends()  # cleanup
+
+
+@pytest.fixture
+def force_aravis_unavailable(monkeypatch):
+    """
+    Force the Aravis backend to behave as if Aravis is not installed.
+    Useful for testing error paths without modifying the environment.
+    """
+    import dlclivegui.cameras.backends.aravis_backend as ar
+
+    # Simulate missing optional dependency
+    monkeypatch.setattr(ar, "ARAVIS_AVAILABLE", False, raising=False)
+    # Make sure the module symbol itself is treated as absent
+    monkeypatch.setattr(ar, "Aravis", None, raising=False)
+    yield
+
+
+@pytest.fixture
+def force_pypylon_unavailable(monkeypatch):
+    """
+    Force Basler/pypylon to be unavailable for error-path testing.
+    """
+    try:
+        import dlclivegui.cameras.backends.basler_backend as bas
+    except Exception:
+        # If the module doesn't exist in your tree, ignore.
+        yield
+        return
+    monkeypatch.setattr(bas, "PYPYLON_AVAILABLE", False, raising=False)
+    monkeypatch.setattr(bas, "pylon", None, raising=False)
+    yield